Isolation of nulcei

Hello,
I'm looking for a protocol for isolating nuclei from cultured human
and rodent cells. I'm after a protocol which does not use detergents,
so that the membranes of the nuclear envelope remain intact. The
protocols I have been using either leave most of the cells
undisrupted, or cause the nuclei to clump. I'm worried that spinning
clumps of nuclei through sucrose to purify them will not do anything
towards removing the cell debris around individual nulcei.
Any ideas ?